Hello,

I use the recent C API of Berkely DB to make a kind of an address book
on Windows, the key/data entries are all saved in unicode format. I
need therefore to provide my own B-Tree comparison function as stated
in the documentation.

I made the same things written there:

int compare_int(DB *dbp, const DBT *a, const DBT *b)
{
int ai, bi;

/*
* Returns:
* < 0 if a < b
* = 0 if a = b
* > 0 if a > b
*/
memcpy(&ai, a->data, sizeof(int));
memcpy(&bi, b->data, sizeof(int));
return (ai - bi);
}

... and put this before opening the DB and after creating it:

dbp->set_bt_compare(dbp, compare_int)

Then I get this failure:

E2034 Cannot convert 'int (* (_closure )(__db *,const __db_dbt *,const
__db_dbt *))(__db *,const __db_dbt *,const __db_dbt *)' to 'int
(*)(__db *,const __db_dbt *,const __db_dbt *)'

E2340 Type mismatch in parameter 2 (wanted 'int (*)(__db *,const
__db_dbt *,const __db_dbt *)', got 'void')


I just wanted to see if this is possible, and eventually to change the
function to whatever suits my program. Any clues?

Regards,
Al

I just tried this (4.3.29 on Windows), and it (this below) compiles for
me:

int mycompare(DB * dbp, const DBT * a1, const DBT * a2)
{
return 1;
}

....
dbp->set_bt_compare(dbp, mycompare);


********

Any chance some macro expansion is plaguing you? (That is just a short
in the dark.)

Hi Al,

Is your source a C++ program using the C API? If so, you'll need:

extern "C" {
int compare_int(DB *dbp, const DBT *a, const DBT *b) {
...
}
}

Also, what compiler are you using?

Regards,
Michael.

* Al:

This looks like as if your compare_int function is some member
function. You should make it a global function, and declare it as
'extern "C"'.